The present telecommunications carrier network has evolved into a primarily digital network with industry standard transmission rates, channelization, multiplexing/demultiplexing, switching and cross-connection. The network includes both copper and optical fiber transmission cables, as well as free space (e.g. microwave) transmission. Mechanical and electronic switches are used. Equipment used to form these networks must conform to very rigid specifications which define interface signal characteristics, signal framing formats, multiplexing techniques and channel clock and jitter characteristics. This allows equipment from a variety of vendors to be used to construct the various carrier networks and to interface to the carrier networks. A high degree of compatibility among the carrier networks is also provided.
In the evolution of the telecommunications carrier network, many network communications problems have been addressed and solved. For example, carrier recovery in a network is described in U.S. Pat. No. 4,458,356 to Toy. The framing of transmitted data for alignment and synchronization within a single channel is described in U.S. Pat. Nos. 4,394,758 to Donne; 4,394,759 to Delle Donne; 4,675,886 to Surie; 4,744,095 to Cornet et al.; and 4,945,533 to Schroeder et al. Substitution of a new channel for a defective data channel is described in U.S. Pat. No. 4,417,348 to Abbruscato.
Standardization of the telecommunications network has often forced users to utilize network channels which have a higher bandwidth, and are therefore more expensive than necessary, because the channel bandwidth in the network cannot be customized. In particular, users of networks must utilize the bandwidth in the basic channel increments which are available from the telecommunications carriers. If a higher bandwidth is required than is provided by a given type of channel, the user is forced to utilize the next higher bandwidth channel even though this bandwidth may far exceed the user's requirements.
An example of the fixed data communications bandwidths which are available to a network user may be found in the "T1" and "T3" standardized channels which are made available by network carriers. The T1 channel, a 1.544 megabit signal, accommodates 1.536 megabits per second of voice and/or data communications. The next higher bandwidth which is widely available for use is the T3 channel, a 44.736 megabit per second signal, which has a payload bandwidth of 44.2 megabits per second. Intermediate rates between 1.536 megabits per second and 44.2 megabits per second are not available. Accordingly, a user application requiring a bandwidth increment greater than 1.536 megabits per second, but less than 44.2 megabits per second, must use a T3 channel at less than full capacity. Since a T3 channel is far more expensive than a T1 channel, the use of a T3 channel at less than full bandwidth is costly, and wasteful of network resources. This is especially true when the user's bandwidth requirement is a small multiple of the available T1 bandwidth, since the bandwidth ratio between the T1 and T3 channels is almost thirty.
It would be desirable to combine two or more T1 channels to obtain the requisite bandwidth. However, channel combining cannot be readily done, because there are no assurances that information transmitted over a plurality of combined channels will be received synchronously. In fact, although the commercial carriers guarantee that information transmitted over an individual channel, such as a T1 channel, will arrive intact, there is no guarantee that information transmitted over combined channels will have any predictable delay or phase relationship. Predictable delay/phase relationships among different channels cannot be assured because each channel may follow a different route through the telecommunications carrier network, even though the channels are transmitted from the same location and received at the same location. The delay differences between a group of channels which follow the same route through the network may be minimal. However, when the channels are routed through different routes on the same network carrier, or are split between different network carriers, the received information will not have a predictable delay/phase relationship.